Tensile and Shear-Mode Cracking of Titanium Sheet in Air and in Salt Water

Crack-propagation tests were conducted using titanium alloy (Ti-6A1-4V) sheet to study the relationship between changes in salt-water cracking behavior and rotation of the crack from a tensile to a shear mode of cracking. Analysis of stress intensity versus cracking rate and examination of electron fractographs for four 16-in. wide panels of Ti-6A1-4V cycled at two stress levels showed a definite change in salt-water cracking behavior occurring at a cracking rate of approximately 260 μ in. per cycle and between the stress-intensity range of 12 ksi √in. and 17.6 ksi √in. The cracking rates in salt water and in air were found to be the same after the crack front had rotated from a tensile to a shear mode of cracking in ten specimens examined including both Ti-6A1-4V and Ti-8Al-Mo-1V.